Convergence insufficiency or convergence disorder is a sensory and neuromuscular anomaly of the binocular vision system, consisting of a reduced ability of the eyes to turn towards each other, or sustain convergence. It is observed a dyssynergia of the ocular movements, in particular a speed difference between both eyes.
The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They may include, but are not limited to, diplopia (double vision), asthenopia (eye strain), transient blurred vision, difficulty in sustaining near-visual function, abnormal fatigue, headache, and abnormal postural adaptation, among others.
One solution for treating a wearer having convergence insufficiency is attending orthoptics sessions. However, visual training may not always work on presbyopic patients.
Another solution consists in compensating for such convergence insufficiency by using a prescription prism for at least one of the wearer's eyes. However, its efficiency may vanish with time and the prism value has then to be increased.
Therefore, there is currently no satisfying solution for an ophthalmic lens wearer who suffers from oculomotor imbalance. This applies in particular for wearers who suffer in addition from presbyopia.
Starting from this situation, an object of the present invention consists in efficiently taking into account the existence of an oculomotor disorder such as the convergence insufficiency when designing a progressive surface.
Another object is avoiding that the troubles caused by convergence insufficiency disturb the patient when performing near-vision tasks.